1. Field of the Invention
The invention relates to runout detection for optical discs, and in particular, to methods for detecting a runout disc in an optical apparatus.
2. Description of the Related Art
During the manufacturing stage of an optical disc, a concentric circling track is formatted for data storage, whereby data are written along the track. When a reading operation is performed, the track is followed confirming that the written data are locatable and accessible. Generally, distances between adjacent tracks, the track pitch, vary with different optical disc standards. For a compact disc (CD), the average track pitch is 1.6 μm. Alternatively, a digital versatile disc (DVD) has an average track pitch of 0.74 μm.
When manufacturing an optical disc, a motor may dig a central hole on the optical disc to facilitate installation. Theoretically, the central hole should be exactly in the center of the concentric circle. In practice, errors are unavoidable. The optical disc is made of polycarbonate, modeled and shaped under certain thermal conditions. Errors of deviation from the center of the central hole of the optical disc may range from 10 μm to 100 μm. The deviation is also referred to as an excentricity or a runout, which may cause track seeking failure where data stored on the optical disc are consequently inaccessible. It is therefore desirable to determine whether an optical disc has runout before reading data from it.